This invention relates to the filtering of micro-particulate matter, i.e. matter having dimensions in the micron range, and more particularly to the filtering of dry toner particles.
In certain kinds of photocopiers, particulate matter, known as "dry toner" and ranging in size from about 1 to 40 microns, is used to form visible images. During this process dust is created which requires filtering.
The filters that are in common use typically employ a porous material and are relatively fragile. Consequently the filters often become damaged during shipment and installation.
Although consideration has been given to the use of a protective layer with such a filter, it has been generally assumed that this would interfere with proper filter functioning.
In addition the filters that are commonly employed for the removal of particulate matter of micron size in, for example, dry toner copier machines, do not provide efficient filtering. They allow a great deal of effluent to pass and they have a tendency to become clogged with particles after only limited usage. As a result, frequent replacement of the filters is necessary.
Moreover the tendency of conventional filters to become clogged after only short usage tends to subject the associated fans to irregular loading. When the filter is first installed and in a relatively unclogged condition air flows through it freely, but as the filter becomes filled with particles, the passage of air is impeded and the work load on the fan is significantly increased. This irregular loading causes both equipment and maintenance problems.
Accordingly, it is an object of the invention to realize a filter system which is suitable for removing the entire range of particulate matter encountered in the use of small size particles, especially those in the micron range.
Another object of the invention is to achieve a relatively durable particulate filter which is less likely to become damaged during shipment and installation.
Still another object of the invention is to improve the loading characteristics of filters so that the life of the filter can be extended considerably beyond the level at which conventional filters become so clogged and unsuitable for further filtering.
A related object is to reduce the maintenance interval during which filter replacement is necessary in order to assure satisfactory performance of machines in which particulate matter is used, especially that in the micron range. Another related object is to achieve a particulate filter which exhibits a substantially uniform loading characteristic over a period of extended use. A further related object is to provide for uniform loading on the equipment used in the filtering of particulate matter of micron size.
Yet another object is to significantly reduce toner effluent in a copier filter system.